Extended Reach: Remote Network Connectivity

July 1, 2010


Trends in Technology, July 2010

footprint

How to establish remote connectivity for a bigger network footprint.


In at least a few of my previous articles I've written about the obvious advantages of having network connectivity at a transmitter site. This time around I'll cover several ways to establish that remote connectivity, how to safely use the public Internet for WAN functionality, and some of the other less obvious considerations you can do once that connectivity is established.

Over the last 10 years the number of ways to establish network connectivity has certainly increased -- mainly in terms of wireless connectivity. Before going there, though, let's review the ways of doing it by wire. With respect to the wireless connectivity I mentioned, many telcos have increased their data capacity to remote mountain tops and other tower farms. Generally speaking, it's much easier to get a T1 to these locations than it used to be. There are a number of ways to take advantage of this. The one most familiar to broadcast engineers is the use of a Harris/Intraplex system with the TDM interface. The CM5 (common module) in this frame has a built-in CSU and interfaces directly with a T1. In the configuration of this unit, a certain number of timeslots are assigned for a set of DS-64NCs (LAN bridge) cards. By way of the LAN bridge, packets that need to get to the far end are allowed through, and those that do not are not. This allows you to effectively extend the network that resides at your HQ (or wherever that one end of the system lives) in a very convenient fashion -- Ethernet on both sides of the bridge.

Harris Intraplex STL Plus

Harris Intraplex STL Plus


If in your case you find that you can afford an entire T1 just for data purposes, then you will find yourself more in the realm of the IT department (which could very well be you anyway, right?). In this case, you would acquire a set of routers that have T1 interfaces along with at least one Ethernet interface. (You may already have a router in-house that has this capability, or at least an empty slot into which a WAN interface can be installed that has a built-in CSU so it connects directly to a T1. You'll still need a router for the far end though.) With the entire T1 in use for your network connectivity, you'll have a 1.536Mb/s connection -- not too shabby. The neat thing now is the capability of allocating timeslots to different networks. It's beyond the scope of this article to describe how it's done, but a router that has multi-link capability (and at least two Ethernet ports) will allow you to do this. Here's the advantage: You could configure the router in such a way that one network allows for nothing but traffic for HD Radio. In this configuration you would allocate just enough timeslots for this -- and the remaining timeslots would then be used for the remote LAN purposes. Now if you (for example) download a PDF manual, you won't need to worry about causing dropouts in your HD Radio stream.

No T1? No problem

Moseley Lanlink HS900D

Moseley Lanlink HS900D


It's certainly possible that your remote site doesn't have T1 accessibility from your local telco, and in that event, you'll need to look at how to make the connection wirelessly. Probably the most well-known equipment for doing this is the Moseley LanLink. Like the Intraplex DS64NC cards, the LanLink functions as a network bridge -- and its interface is Ethernet on both ends. The LanLink provides up to a 1Mb/s data rate. Perhaps the most convenient aspect of the LanLink is that it operates in the 900MHz ISM band, so by way of a set of duplexers, you can use the 950MHz antennas already in place.

I should also mention that you could roll your own 900MHz ISM-band system. A few minutes of research on the Internet will reveal a number of companies that make transceivers for that band with Ethernet interfaces. Duplexers can be used with an established 950MHz link, or you could simply find some directional antennas for that band and make a new link.

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Trends in Technology, July 2010

Broadcast Electronics Big Pipe LT

Broadcast Electronics Big Pipe LT


Another way to establish network connectivity at a remote site is by way of the higher ISM bands -- 2.4, 5.3 and 5.8GHz. One of many possibilities in terms of equipment for that would be the Broadcast Electronics Big Pipe LT, which is basically a set of transceivers that work in said ISM bands. Big Pipe establishes a 45Mb/s (T3) data connection in both directions, therefore opening up lots of capability.

The ISM bands are unlicensed, of course, so keep in mind that you may have to contend with other users for spectrum. Take care in the path design.

4G connections

As time has moved along, many of us have established Internet connections at home based on cable (or even DSL) connections -- and so the connections described thus far may seem kind of slow. In the larger metro areas, there are new companies that are providing connections based on 4G technology that will allow much faster connections to the Internet. Now keep in mind that is not the same as an extension of your LAN. (More about that below.)

One company that has a big presence in New York City is Towerstream, an ISP that provides the actual connection via a point-to-point radio link between one of its sites (such as the Empire State Building) and your office. According to the company website, it can provide anything from T1 speed up to 1.5Gb/s (that should be more than enough, right?). Towerstream started in Providence, RI, and appears to be growing in a westerly fashion.

Another company that is getting quite a bit of buzz is Clearwire. Clearwire is more oriented toward personal or "SOHO" (small office/home office) applications. The modem it provides is obviously a transceiver that needs to be located so it can see the best Clearwire network node. The output side of the modem looks just like a modem that we'd be accustomed to seeing from a cable TV feed. Its interface is Ethernet, it has an on-board DHCP server, and by use of a small Ethernet switch, you can connect multiple hosts to it.

Of course, depending upon the situation, you may find some other way to get a connection to an ISP. Perhaps cable TV is an option at your transmitter site (since many sites are practically in residential neighborhoods) or perhaps you can get DSL easily enough. Whatever the case, after making the connection work, you are left with an easy way to get out to the Internet, but nothing else; you can surf the Internet, and you can download manuals and whatnot -- but you won't be on your HQ network. No access to the company e-mail server, your VoIP phone system, or any number of other servers or hosts that you would be able to reach if you were on a private connection to your LAN.

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Trends in Technology, July 2010

VPN

As you probably imagined, there is a fairly easy solution to this problem as well, known as VPN (virtual private network). Many of us use temporary VPN connections from home to get network access as necessary; but you can set up what amounts to a permanent connection from a remote site, to your HQ network, by way of the public Internet by use of VPN as well. One possible solution (out of many) is to use a Cisco SR-520T1 router at your HQ (in the case that you had a T1 connection from your ISP) and at the remote end, a Cisco RVL200. Just one other possible solution would be the use of two Netgear FVS318s -- one would be located at your HQ, and the other at your remote site.

Finally, let your imagination run wild and think about some of the extra functionality you can enjoy after getting a good network connection at your remote site. Probably the most obvious one is e-mail. Not just the text now, mind you: Quickly download all the links people send you. Download a PDF of a piece of equipment at the site. Put an extension of your VoIP phone system at the transmitter site. Install IP/video cameras looking at the front door or gate. Locate any number of backup servers at the transmitter site. Allow yourself remote access to any and all embedded Web servers that live in so many pieces of equipment we use. Start using SNMP (Simple Network Monitoring Protocol) remote controls. Use NTP (Network Time Protocol) to synchronize all the various time references that live at the site, so when you go back and look at error logs, all the times match up. Maybe even an audio stream for a backup STL.

Little stuff like that.

It's about time broadcasters started catching up with the rest of the communications world in the way we use networks and the Internet. The possibilities seem just about endless.


Terms

LAN: local area network

WAN: wide area network

LAN bridge: A device that makes a physical connection between two networks that are of the same subnet. One end of the bridge is connected (typically by Ethernet) on one network (at the headquarters for example) and the other end at a different location remote from HQ. As the LAN bridge receives Ethernet frames on its network interface, it writes the source and destination MAC addresses into its MAC address table. In this way it learns where hosts are located; and when hosts on one end need to reach the other end of the bridge, it passes those packets through. It does not pass packets that don't need to reach the other end.

VPN: virtual private network. There are two important aspects of network security dealt with by way of VPN. The first is authentication: A router at the HQ will be able to authenticate a remote source of packets as being one that is legitimate. This prevents unauthorized users from accessing a private network. The second is encryption. By encrypting the payload data in the packets sent between two ends of a VPN connection, no one in between will be able to read them. So, in using both authentication and encryption, it's possible to use the public Internet for private network connectivity.


Resource Guide

  • Broadcast Electronics
  • Cisco
  • Clearwire
  • Harris Intraplex
  • Moseley
  • Netgear
  • Towerstream

    Irwin is transmission systems supervisor for Clear Channel NYC and chief engineer of WKTU, New York. Contact him at doug@dougirwin.net.



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